In recent years, a number of electronic devices that contactlessly transmit electric power have been developed. In order to transmit electric power contactlessly among electronic devices, a magnetic field coupling type electric power transmitting system is often employed in which a coil module is provided in each of an electric power transmitting unit (electric power transmitting apparatus) and an electric power receiving unit (electric power receiving apparatus).
In the magnetic field coupling type electric power transmitting system, however, the magnitude of a magnetic flux that passes through each of the coil modules is greatly affected by electromotive force. Thus, in order to transmit electric power with high efficiency, the position of the coil module in the electric power transmitting unit (primary side) relative to the position of the coil module in the electric power receiving unit (secondary side) along a planar direction of the coils needs to be controlled with high precision. In addition, since the coil modules are used as coupling electrodes, it is difficult to reduce the size of the electric power transmitting unit and the electric power receiving unit. Furthermore, for electronic devices, such as a portable device, an effect of heat, radiated from a coil, on a storage battery needs to be considered, which may pose a problem that such an issue is a bottleneck in the layout design.
Thus, electric power transmitting systems that utilize, for example, an electrostatic field are being developed. Patent Document 1 discloses a transmitting system that achieves high electric power transmission efficiency by causing a coupling electrode in an electric power transmitting unit and a coupling electrode in an electric power receiving unit to generate capacitive coupling. Furthermore, Patent Document 2 discloses a capacitive coupling type charger that includes rectangular coupling electrodes disposed in a lattice pattern on a surface of an electric power transmitting stand (electric power transmitting apparatus) on which a portable terminal (electric power receiving apparatus) is to be placed, and carries out control such that electric power is supplied to coupling electrodes disposed in an area where the electric power receiving apparatus is placed.
FIG. 16 is a schematic diagram illustrating configurations of existing electric power transmitting systems. FIG. 16(a) is a schematic diagram illustrating a configuration of an electric power transmitting system that employs asymmetric capacitive coupling. As illustrated in FIG. 16(a), an electric power transmitting unit (electric power transmitting apparatus) 1 includes a large-sized passive electrode 3, a small-sized active electrode 4, and a power supply circuit (power supply) 100, and an electric power receiving unit (electric power receiving apparatus) 2 includes a large-sized passive electrode 5, a small-sized active electrode 6, and a load circuit 24. High electric power transmission efficiency is achieved by generating a strong electric field 7 across the active electrode 4 of the electric power transmitting unit 1 and the active electrode 6 of the electric power receiving unit 2.
FIG. 16(b) is a schematic diagram illustrating a configuration of an electric power transmitting system that employs symmetric capacitive coupling. As illustrated in FIG. 16(b), an electric power transmitting unit (electric power transmitting apparatus) 1 includes a plurality of active electrodes 4 and a power supply circuit (power supply) 100, and an electric power receiving unit (electric power receiving apparatus) 2 includes a plurality of active electrodes 6 and a load circuit 24.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-296857
Patent Document 2: European Patent No. 1689062
FIG. 17 is a schematic diagram illustrating the configuration of the existing capacitive coupling type charger disclosed in Patent Document 2. In FIG. 17, rectangular coupling electrodes 4 are disposed in a lattice pattern on a surface of an electric power transmitting stand (electric power transmitting apparatus) 1 on which a portable terminal (electric power receiving apparatus) 2 is to be placed, and a switching circuit 104 switches a state of connection between the coupling electrodes 4 and a power supply circuit 100 so that electric power is supplied to those coupling electrodes 4 disposed in an area where the electric power receiving apparatus 2 is placed. In the capacitive coupling type charger illustrated in FIG. 17, electric power is transmitted with the use of symmetric capacitive coupling illustrated in FIG. 16(b), and a connection between a coupling electrode 4 and two voltage terminals of reverse polarities is controlled to be turned on/off. In a case in which asymmetric capacitive coupling illustrated in FIG. 16(a) is to be employed, however, a connection between a coupling electrode 4, and active voltage terminals and passive voltage terminals of reverse polarities, or reference potential terminals needs to be controlled to be turned on/off. Patent Document 2 does not disclose the on/off control of the connection with the active voltage terminals, the passive voltage terminals, or the reference potential terminals, or a specific configuration of the electric power transmitting apparatus 1 that carries out such on/off control.